Centercore process for gas assisted injection molding

ABSTRACT

The present invention comprises a method for delivering a medium such as a gas, vapor or liquid into a melted plastic in a mold via an elongated screw shaft rotatably supported in a housing, the method including the steps of providing the screw shaft with a bore longitudinally therethrough from a proximal end to a distal tip end thereof, rotating the screw shaft in the housing to move plastic therethrough, and into the mold, introducing a gas, vapor or liquid into the bore, to permit the gas, vapor or liquid to be delivered through the bore, and into the molten plastic in the mold through the distal tip end of the screw shaft.

This Application is a Divisional Application of our earlier filed U.S.patent application Ser. No. 08/511,055, filed Aug. 3, 1995, now U.S.Pat. No. 5,670,112 which is incorporated herein by reference in itsentirety, which is a Continuation-in-Part of our earlier filedapplication Ser. No. 08/393,200 filed Feb. 23, 1995, now abandoned,which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the simultaneous or sequential introduction ofmultiphase matter into a plastic melt through a plasticating screw.

2. Prior Art

Heretofore, plastic in molds or dies have been treated by introductionof matter through the wall of the mold, for cooling or the like, ormatter has been added only to the plastic as it is worked between theplasticating screw and the housing in which it is rotatively supported.

BRIEF SUMMARY OF THE INVENTION

The present invention discloses a novel way to introduce high pressuregas, vapors and/or liquids into the process of manufacturing plasticmaterial by a plasticating screw machine. The invention comprisesdrilling (coring) a hole axially through a plasticating screw ofappropriate size to accommodate the introduction of gas, vapors and/orliquids into the melt shot.

A non return shut off valve may be arranged on the tip of thatplasticating screw, which valve is made with a drilled hole through itincluding the tip so that during or after the injection phase (shortshot) or in the process of completion the tip opens either due to airpressure, mechanical actuation (spring loaded) etc. to allow the assistgas, vapors or liquids to hollow out the plastic part, where that screwis utilized in an injection molding operation. A finely controlled gas(typically nitrogen) pressure and volume may be applied to the driving(proximal) end of the plasticating screw by means of a rotationalcollar. The gas will pass through the length of the screw to the nonreturn shut off valve, or tip, where it will enter the molten plasticmaterial. Required gas volume or material viscosity may necessitate finegas entry apertures such as with a jewelled orifice and/or a gas checkvalve to prevent material from blocking gas passages. A typicalprocessing sequence will be incorporated to the gas cycle. The part willbe a short shot. The screw will remain fully forward through the secondstage while gas is applied (no cushion). After this phase, allowancesmust be made for venting or degassing of the unnecessary gas before thepart is ejected, when utilized in an injection molding format. Theintroduction of gas, vapors, or liquids into the plasticating screw isfrom the rear of the screw in one embodiment, or from a design matedentry point, such as a radial channel from a collar radially outwardlyof the screw and into the core of the reciprocating injection screw in afurther embodiment. Assist media is proportionally regulated via thedescribed gas control system to allow for maximum efficiency ofprofiling.

A description of the mechanical aspects of⁻ the invention includes: (a)Injection screw coring for the introduction of gas, vapor, or liquids(fluids); (b) Non return shut off valve threaded onto the delivery endof the plasaticating screw for the purpose of: (1) shuting off thebackflow of the molten plastic during an injection, holding and coolingphase of the plastic, (2) Enhancing the mixing of the molten plastic,(3) Allowing for the passage of high pressure gas, vapors or liquidsthrough the center hole drilled (to specific size) through the center ofthe injection screw tip (aka non return valve), (4) Prevent plasticcoming into center core during the screw recovery or plastificationphase.

The center bore in the plasatication screw is arranged to accommodatethe passage of gas, vapor, liquids through the screw injection tip undercertain pressures and temperatures. The center core hole should also beable to accommodate single, double or multiphase coaxial tubes for thepassage of multiphase materials with a conveying point in the injectiontip. Temperature control is of paramount value for the constituentplastics being worked.

A high pressure rotary union may be arranged at the back end of thescrew depending as to whether constituents are introduced axially orradially.

The phase process for injection molding plastics utilizing the centercored screw comprises: (a) Injection phase: control by a control circuitof the melt and high pressure gas, vapor, or liquid and temperaturecontrol thereof, (b) Holding and Cooling phase: control of gas, vapor,or liquid pressure and temperature for efficient cooling of the moldedparts to control surface finish and part shrinkage. This is accomplishedby: (1.) Introduction of gas, vapor, or liquid simultaneously (without atime delay) using control circuit components comprising a furtherembodiment of the present invention; or (2.) Introduction of gas, vapor,or liquid sequentially (after a preprogrammed time delay) the controlcircuit components of the present invention; (3.) Temperature control ofthe gas to provide an optimal "gas bubble", coring, or tunneling, orthereof into the plastic melt; and (4.) Profiling of gas pressure by useof software with a programmed capability to ramp or step up the gaspressure using a menu driven system allowing various time/pressuredurations in the gas injection phase.

A PID (proportional integral derivative) controlled micro-controller,comprises a further embodiment of this invention. This ProportionalController is a closed loop PID controlled pressure regulating system,having a digital (LCD) display used as an attachment to commerciallyavailable gas control systems.

The proportional control is achieved through an electro-pneumaticcircuit with a proportional regulator (or valve) pilot operating abooster unit which then pilot operates a high pressure regulator. Lowpressure compressed air 0.55-0.70 MPa (typically 80-150 psi) is used asa control pressure which then regulates the pressurized gas to desiredlevels up to a maximum of 103 MPa (˜15,000 psi max.). With this system,as the low pressure signal is boosted to the respective high pressuresetting, it "loads" a "dome loaded" high pressure regulator. Theproportional regulation is controlled by a Pulse Width Modulating (PWM)controller operating a normally closed on/off three way valve . Upon thecompletion of the cycle, the line pressure from the gas tubing can bevented through a vent port in the "dome" regulator.

A downstream high pressure transducer attached to the gas line providesfeedback to the micro-controller thus adjusting the PWM proportionalvalve to the set point (closed loop). This closed loop system with afull PID control algorithm and controlled by the micro-controller allowsthe gas pressure to be controlled via a voltage (or current) profilethus creating an infinite number of pressure versus time settings. Anon-board RS232 interface allows the capability to capture theinformation from the gas pressure transducer before the gas enters themold and thus may be used as a monitoring and statistical tool. A PCdisplays a menu system, where pressure can be profiled either up or downas a geometric function.

A digital display is arranged to show the pressure set point and theactual value (during cycle). The micro-controller (PWM) is driven usinga separate 0-24 VDC, 4.0 amps max. rated regulated power supply. Portsfor the pressure sensor, RS232, allow for data acquisition and valvecontrol signals (#1, #3, #5, #6) allow voltage input into the controllerboard. Using the up/down keys, the pressure settings are easily adjustedwithin a pressure sensitivity scale of ±1 psi and can be seen on screenas setpoint vs. actual. Adjustments to the software are made usingdiagnostics modeand coarse adjust. The response time of the PIDcontroller from the start of the cycle to reaching the setpoint isapproximately 50 milliseconds (response time can be adjusted to specificneeds).

A prototype of the micro-controller is currently used with the gascontrol system on for example, a 250 Ton 32 oz. Cincinnati Milacroninjection molding machine as an added feature to study the processparameters of the gas-assisted injection molding process.

A Gas-Assist Controller system will be attached to an existingcommercial gas unit utilizing the volume controll technique and will beoperational as an integrated attachment. The system has features formultiple independent channels (if needed), closed loop control, 0-5 VDCcontrol signals, PID control algorithm, pulse width modulating (PWM)outputs, option for extra pressure transducers, input signalconditioning, RS232 monitor, and operator interface (Keyboard/LCD).

Equipment operation for gas heating/cooling by this system would allowfor pressurization of N₂ by the gas (N₂) itself or shop air (150 psi),whichever suits per need.

If N₂ is not used as a control mechanism, a Tee fitting and gasregulator would be eliminated from the overall system operation. A highpressure gas (up to 15,000 psi) may be used as both the controlmechanism as well as the actual set pressure gas to hollow out themolten plastic. A proportional regulator is arranged to provide precisepressure control with a flow control valve loading a "Dome" loaded highpressure regulator to make the gas setpoint (set on the PID controller).A second Tee fitting may be used as a split for the gas injection stageand the gas packing/holding/cooling state.

During the gas injection stage, once the gas has reached the setpoint atthe "dome" regulator, a first circuit would allow the actuation of a 2way solenoid valve. At this point, a heat exchanger heating element ofthe system would heat the gas to a desired set temperature and fill thegas into the accumulator. At this point, both the pressure and thetemperature would be measured by a pressure transducer and a temperaturesensor. Next, a solenoid valve is arranged in the system to open andallow the free passage of pressurized gas through a fixed jewel orificeand into the mold cavity. A pressure sensor and a temperature sensor maybe placed before the jeweled orifice to measure the pressure andtemperature just before the gas enter the mold.

Upon the completion of gas injection cycle, the solenoid valves arearranged to close. The N₂ would now be diverted to a second circuitwhere a humidifier device may add small amounts of H₂ O to the N₂ andthe components would be cooled to a set temperature by a heat exchangercooling element in the system. Again, a 2 way solenoid valve is arrangedto open, allowing the mixture to pass through the orifice with pressuresensor and temperature sensor recording the pressure and temperature ofthe cold mixture. This phase of the cycle would assist in making hollowinjected molded parts.

Thus the invention includes: (1) a gas injection molding systemcomprising a screw for delivering plastic material to a mold and a gasinjection jeweled orifice port through the screw tip for injecting gas,vapor, or liquids into the plastic in the mold; (2) a gas injectionclosed loop pressure control system using a dome regulator ratio devicewith a micro-processor based control system to profile (ramp/step) thegas injection using a menu driven system allowing various time/pressuredurations in the gas injection phase and the gas holding/packing phase.This can be either a personal computer (PC), Programmable Logiccontroller (PLC) or an embedded system with either a ProportionalIntegral Derivative (PID) or FUZZY logic algorithm; and (3) a controlsystem for controlling the temperature of the gas during the injectionphase and cooling phase.

The invention further includes a control for the injection stagevelocity of the gas. A controlled pressure in a tank is arranged todeliver a controlled velocity through a fixed jeweled orifice. Due tothe sonic flow of gas If, P1+1.013<=1.896 (P2+1.013) then the flow rateis dependent only on the orifice size and supply pressure, P1!.

The temperature of the gas may be heated by a heater. This will increasethe gas viscosity thus limiting or helping prevent "gas blow out" fromthe molded part during the process cycle. It will also add to thetemperature uniformity which will decrease the tendency of the part tohave sink marks due to the thermal differences between the melt, moldand gas.

Once the mold has been filled and the part has been properly cored outwith gas, pressure control is necessary to keep the part "packed" andreduce the sink effect. This will be accomplished by switching to thesecond portion (part B) of circuit which regulates pressure only. Thiswill allow for pressure profiling in the holding/packing phase dependingupon the part geometry and material. Simultaneously we will beintroducing water (H₂ O) to the nitrogen (N₂) mixture. This will enterthe hollow core of the part thus providing a faster cooling phase,leading to a decrease in cycle time. The after cooler may not benecessary as the effect of phase change of liquid to steam of the H₂ Omay remove sufficient heat.

It is proposed to inject other gases into the plastic hollow part onceit has expanded. A number of gases can be used. One such effective wayis to have a phase change in the part for doing the cooling. A mixtureof cold air with water spray will convert the spray into ice crystalswhich are conveyed with the air and once they hit the inside of theplastic part the ice will convert the water vapor with a large latentheat of sublimation (about 1100 Btu/lb). As the ice sublimates, thepressure will increase and a control device will allow the part to bevented via a pressure regulator after which the process of air/iceinjection is repeated until the part is sufficiently cooled.

Alternatively one can inject liquid CO₂ (>=80 psi). The liquid turns todry ice at P<=80 psi and then vaporizes (sublimates) when it contactsthe internal wall of the part. A third method would be to use liquidnitrogen. The liquid would evaporate and extract heat from the inside ofthe part. Also, the nitrogen (N₂) could be recovered.

In the present invention. The hydraulic injection cylinder is coupled tothe screw shank for inject and retract functions. The screw shank mayalso pass through a gearbox which provides rotation during plasticizing.The flight includes feed, transition, and metering sections of thescrew. The screw tip or valve will typically incorporate a check ring orball.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will become moreapparent when viewed in conjunction with the following drawings, inwhich:

FIG. 1 is a side elevational view of a plasticating machine assembly,partly in section;

FIG. 2 is a side elevational view of a plasticating screw with a valveshown arranged on its distal tip end;

FIG. 3 is a longitudinal sectional view taken of a plasticating screwshowing both radial entry and axial entry embodiments for delivery ofgas into the axial center core for introduction into a plastic meltthrough the screw tip;

FIG. 4 is an exploded view of a plasticating screw with a non-returnvalve on its distal end;

FIG. 5 is a side elevational view of a non-return valve;

FIG. 6 is a schematic view of a ball check valve;

FIG. 7 is a side elevational view of a non-return valve and portions ofa screw shaft therewith;

FIG. 8 is a schematic representation of the control circuit for thepresent invention;

FIGS. 9a and 9b represent schematic and panel layouts of the controllerportion of the control circuit of the present invention;

FIG. 10 is a block diagram for one channel of the controller of thepresent invention;

FIG. 11 is a schematic diagram of gas supply components for the presentinvention; and

FIG. 12 is a schematic representation of the components for heating andcooling gas utilized with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings in detail, there is shown a sectional viewof a reciprocating screw injection molding machine 10 arranged tointroduce high pressure gas, vapors or liquids to assist injectionmolding of plastic material. This process is based on drilling (coring)a hole 12 axially through a reciprocating plasticating screw 14 as shownin FIG. 2, the hole 12 being of appropriate size to accommodate theintroduction of gas, vapors or liquids into the melt shot. Also, a nonreturn shut off valve 16, as may be seen on the distal tip of the screwin FIG. 2, and shown also in FIG. 4, is shown more completely in FIGS.5, 6 and 7, would be made with a drilled hole 18, through it, includingthe tip 20, so that during or after the injection phase (short shot) orin the process of completion the tip 20 opens either due to airpressure, mechanical actuation (spring loaded) etc. to allow the assistgas, vapors or liquids to hollow out a plastic part being manufactured.A finely controlled gas (typically nitrogen) pressure and volume may beapplied to the driving end 22 of the screw 24 by means of a rotationalcollar 25, where possible, as may be seen in FIG. 3. The gas will passthrough the length of the screw 24 to the non return shut off valve, ortip 26, where it will enter the molten material. Required gas volume ormaterial viscosity may necessitate fine gas entry apertures and/or gascheck valving to prevent material from blocking gas passages. A typicalprocessing sequence will be incorporated to the gas cycle. The part willbe a short shot. The screw 24 will remain fully forward through thesecond stage while gas is applied (no cushion). After this phase,allowances must be made for venting or degassing of the unnecessary gasbefore the part is ejected. The introduction of gas, vapors, or liquidsis from the rear (or design mated radial entry point to the core of thereciprocating injection screw, as described hereinbelow), and assistmedia is proportionally regulated via the described gas control systemto allow for maximum efficiency of profiling.

The injection screw hole should accommodate the passage of gas, vapor,liquids through the screw injection tip under certain pressures andtemperatures. The center core hole 12, as shown for example in FIG. 2,should also be able to accommodate single, double or multiphase coaxialtubes 32, and 34, for the passage of multiphase materials with aconveying point in the injection tip. Temperature control is ofparamount value for the constituent.

A high pressure rotary union 36 is attached at the back (proximal) endof the screw 24, shown in FIGS. 3 and to the back of the screw 14, inFIG. 4, whether constituents are introduced axially or radially.

A closed loop PID controlled pressure regulating system 40, is shown inschematic form, in FIG. 8, with a digital (LCD) display may be used asan attachment to a commercially available gas control systems.

The proportional control is achieved through an electro-pneumaticcircuit with a proportional regulator (or valve) 41 pilot operating abooster unit through which the pilot operates a high pressure regulator47. A low pressure compressed air 0.55-0.70 MPa (typically 80-150 psi)source 11, is used to control pressure which then regulates thepressurized gas to desired levels up to a maximum of 103 MPa (˜15,000psi max.). With this system, as the low pressure signal is boosted tothe respective high pressure setting, it "loads" the "dome loaded" highpressure regulator 47. The proportional regulation is controlled by aPulse Width Modulating (PWM) controller 42 operating the normally closedon/off three way valve 41. Upon the completion of the cycle, the linepressure from the gas tubing can be vented through a vent port 48 in the"dome" regulator.

A downstream high pressure transducer 46 attached to the gas lineprovides feedback to the micro-controller thus adjusting the PWMproportional valve to the set point (closed loop). This closed loopsystem with a full PID control algorithm and controlled by themicro-controller allows the gas pressure to be controlled via a voltage(or current) profile thus creating an infinite number of pressure versustime settings. An on-board RS232 interface unit 43 allows the capabilityto capture the information from the gas pressure transducer before thegas enters the mold 45 and thus be used as a monitoring and statisticaltool. A PC may display a menu system, where pressure can be profiledeither up or down as a geometric function.

A digital display panel 50 shown in FIG. 9b shows the pressure set pointand the actual value (during cycle). The micro-controller (PWM) isdriven using a separate 0-24 VDC, 4.0 amps max. rated regulated powersupply 57, as shown in FIG. 9a. Ports for the pressure sensor 55, andRS232 54, allow for data acquisition. Valve control signals 56 allowvoltage input into the controller board. Using the up/down keys 61 and62 shown in FIG. 9b, the pressure settings are easily adjusted within apressure sensitivity scale of ±1 psi and can be seen on screen 68 assetpoint vs. actual. Adjustments to the software are made usingdiagnostics mode switch 69 and coarse adjust switch 71. The responsetime of the PID controller from the start of the cycle to reaching thesetpoint is approximately 50 milliseconds (response time can be adjustedto specific needs).

The logic diagram of the micro-controller is shown in FIG. 10. Aprototype of the micro-controller is currently used with the gas controlsystem for example, on a 250 Ton 32 oz. Cincinnati Milacron injectionmolding machine as an added feature to study the process parameters ofthe gas-assisted injection molding process.

FIG. 11 is a schematic diagram of a gas supply system 76 for the presentinvention. The system 76 may be attached to an existing commercial gasunit utilizing the volume controlled technique and may be operational asan integrated attachment.

The system 76, as shown in FIG. 12, may be arranged to operate and allowfor pressurization of N₂ by the gas (N₂) itself or shop air (150 psi),whichever suits the need.

If N₂ is not used as a control mechanism, the Tee fitting 81 and gasregulator 82 would be eliminated from the overall system operation. Thehigh pressure gas (up to 15,000 psi) would be used as both the controlmechanism as well as the actual set pressure gas to hollow out themolten plastic. A proportional regulator would provide precise pressurecontrol with a flow control valve loading a "Dome" loaded high pressureregulator 85 to make the gas setpoint (set on the PID controller).Another Tee fitting 86 would be used as a split for the gas injectionstage, shown as the first circuit "A", in FIG. 12, and the gaspacking/holding/cooling state, shown as the second circuit "B" in FIG.12.

During the gas injection stage, once the gas has reached the setpoint atthe "dome" regulator 85, circuit A would allow the actuation of a 2 waysolenoid valve 87. At this point, a heat exchanger heating element 88would heat the gas to a desired set temperature and fill the gas intothe accumulator 89. At this point, both the pressure and the temperaturewould be measured by a pressure transducer 98 and a temperature sensor99. Next, a solenoid valve 90 would open and allow the free passage ofpressurized gas through a fixed jewel orifice 101 and into the moldcavity 95. A pressure sensor 96 and a temperature sensor 97 would beplaced before the jeweled orifice 101 to measure the pressure andtemperature just before the gas enter the mold 95.

Upon the completion of gas injection cycle, the solenoid valves 90 and87 would close. The N₂ would now be diverted to circuit B where ahumidifier device 92 would add small amounts of H₂ O to the N₂ and thecomponents would be cooled to a set temperature by a heat exchangercooling element 93. Again, a 2 way solenoid valve would open 94 allowingthe mixture to pass through the orifice 101 with pressure sensor 96 andtemperature sensor 97 recording the pressure and temperature of the coldmixture. This phase of the cycle would assist in making hollow parts.

Thus the present invention includes a gas injection molding systemcomprising a screw for delivering plastic material to a mold. It alsoincludes a gas injection jeweled orifice port through the screw tip forinjecting gas, vapor, or liquids into the plastic being molded.

The gas injection may use a menu driven system allowing varioustime/pressure durations in the gas injection phase and the gasholding/packing phase. This can be either a personal computer (PC),Programmable Logic controller (PLC) or an embedded system with either aProportional Integral Derivative (PID) or FUZZY logic algorithm. Thetemperature of the gas may be controlled during the injection phase andcooling phase via the control system.

I claim:
 1. A method for injection molding in which a gas, vapor orliquid is delivered into a melted plastic downstream of an elongatedscrew shaft having a longitudinal axis, which screw shaft is rotatablyand reciprocably supported within a housing of an injection moldingmachine, said screw shaft having a proximal end and a distal tip end,said delivery arranged to effect changes within that plastic, saidmethod comprising the steps of:providing a bore through said screw shaftfrom said proximal end to said distal tip end and out through saiddistal tip end; rotating said screw shaft in said housing to drive saidplastic along a path between said screw shaft and said housing, anddownstream of said screw shaft; moving said reciprocably movable screwshaft along its longitudinal axis in said injection molding machine; andintroducing said gas, vapor or liquid into said bore to permit said gas,liquid or vapor to be delivered through said bore of said screw shaftand out said distal tip end thereof, and into said melted plastic forinjection into a mold by said reciprocably movable screw shaftdownstream of said screw shaft.
 2. The method of injection molding inwhich a gas, vapor or liquid is delivered into a melted plasticdownstream of an elongated screw shaft in said injection moldingmachine, as recited in claim 1, including the step of:attaching acoupling to said reciprocably movable screw shaft in communication withsaid bore, to permit said gas, vapor or liquid to be delivered throughsaid bore, and into said melted plastic at said distal tip end of saidscrew shaft.
 3. The method of injection molding in which a gas, vapor orliquid is delivered into a melted plastic downstream of an elongatedscrew shaft in said injection molding machine, as recited in claim 2,including the step of:arranging at least one conduit spaced within saidbore of said reciprocably movable screw shaft, so as to permit separatetransfer of multiple gases, liquids or vapors simultaneously into saidplastic melt at said distal end of said screw shaft.
 4. The method ofinjection molding in which a gas, vapor or liquid is delivered into amelted plastic downstream of an elongated screw shaft in said injectionmolding machine, as recited in claim 1, including the stepof:introducing said gas, liquid or vapor sequentially through said boreand into said melted plastic downstream of said reciprocably movablescrew shaft, so as to introduce a bubble of said gas, liquid or vaporinto said melted plastic at said downstream end of said screw shaft. 5.The method of injection molding in which a gas, vapor or liquid isdelivered into a melted plastic downstream of an elongated screw shaftof an injection molding machine, as recited in claim 2, including thestep of:providing a radially directed opening from said bore to saidcoupling to provide fluid communcation from said coupling to said distaltip end of said screw shaft.
 6. A method for the delivery of at leastone fluid into a melted plastic in a mold downstream of an elongatedscrew shaft in an injection molding machine, which screw shaft isrotatably and reciprocably movably supported within a housing, saidscrew shaft having a proximal end and a distal tip end, said delivery ofsaid fluid arranged to effect changes to that plastic, said methodcomprising the steps of:providing a bore through said screw shaft fromsaid proximal end to said distal tip end and out through said distal tipend thereof; rotating said screw shaft in said housing to drive plasticabout said screwshaft and into said housing downstream of said screwshaft; reciprocably moving said screw shaft in said housing in saidinjection molding machine to inject plastic into said mold; andintroducing said fluid into said bore to permit said fluid to bedelivered through said bore and out said distal tip end of saidreciprocably movable screw shaft and into said molten plastic at thedownstream end of said screw shaft; and injecting said fluid into saidmold.
 7. The method for the delivery of at least one fluid into a meltedplastic downstream of an elongated, reciprocably movable screw shaft ofan injection molding machine, as recited in claim 6, wherein said fluidis selected from the group consisting of: a gas, a liquid or a vapor. 8.The method for the delivery of at least one fluid into a melted plasticdownstream of an elongated screw shaft of an injection molding machineas recited in claim 6, including the step of:introducing said fluid intosaid bore through a coupling attached to said reciprocably movable screwshaft.
 9. The method for the delivery of at least one fluid into amelted plastic downstream of an elongated screw shaft of an injectionmolding machine as recited in claim 8, including the step of:attachingsaid coupling to said reciprocably movable screw shaft at said proximalend of said screw shaft.